The C>T mutation at position-101 from the cap site, within the distal CACCC box, is described as the most common silent β-thalassemia mutation in Mediterranean populations.

Amongst 33 mild β-thalassemia intermedia patients referred to our unit as β-thalassemia/ β-silent, 16 had inherited the -101 C>T mutation from one parent, implicating that it is the most common single silentβ-thalassemia mutation in Greece. Through routine DNA screening ofβ-thalassemia carriers, a further 18 β-101 C>T heterozygotes were identified. Strict assessment of clinical, hematological and biosynthetic findings in these 34 heterozygotes demonstrate that, in fact, only 12/34 carriers of this mutation were clinically and hematologically silent; only globin chain synthesis was slightly unbalanced. The remaining 22/34 carriers presented hemoglobin A2 values between 3.7-5.1% and with one exception normal red cells indices and hemoglobin F values. The mean values in all 34 cases were: Hb 13.5 g/dl, Ht 41.4%, MCV 86.6 fl, MCH 28 pg, HbA2 3.5%, HbF 1.7%,α/nona 1.43). In addition, 6/22 of the high HbA2 b-101 carriers had increased red cells osmotic fragility.

In conclusion, only 1/3 of the carriers of the C>T mutation at position-101 were phenotypically silent when hematological findings were assessed with strict criteria. This observation is useful for hematology laboratories involved in β-thalassemia carrier screening.